2011ApJ...735...85S

We present the result of the analysis of the gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by two adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling the light curve considering the parallax effect and Keplerian orbital motion, we are able to not only measure the physical parameters but also to find a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance of 6.7±0.3 kpc from the Earth. The individual lens components with masses 0.9±0.3 M_☉ and 0.5±0.1 M_☉are separated with a semi-major axis of a = 2.5±1.0 AU and orbiting each other with a period P = 3.1 ± 1.3 yr. This event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.